Method of controlling battery charge level of hybrid electric vehicle

ABSTRACT

A method of controlling a battery charge level of a hybrid electric vehicle includes: monitoring a quantity of current accumulated for a predetermined time based on a battery charge/discharge current value; calculating a regenerative charge derating constant; calculating a correction coefficient based on the quantity of current accumulated and a battery state of charge; multiplying the regenerative charge derating constant by the correction coefficient to calculate a final regenerative charge derating constant; and multiplying the final regenerative charge derating constant by a charge power to calculate a final charge power, and selectively restricting the battery charge level based on the final charge power.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.11/850,448, filed Sep. 5, 2007, which claims priority to Korean PatentApplication No. 10-2006-0125253, filed in the Korean IntellectualProperty Office on Dec. 11, 2006, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of controlling a batterycharge level of a hybrid electric vehicle. More particularly, thepresent invention relates to such a method which can selectivelyrestrict the battery charge level to prevent excessive increase inbattery temperature.

(b) Background Art

The term “hybrid vehicle,” in its broadest sense, refers to a vehiclethat utilizes at least two different kinds of power sources. Usually,the term refers to a vehicle that uses fuel and an electric motor,driven by a battery. Such a vehicle is more precisely called a hybridelectric vehicle (HEV).

The hybrid electric vehicle can take on many various structures. Mosthybrid electric vehicles are either parallel type or series type.

The parallel type hybrid electric vehicle is configured such that theengine charges the battery and also directly drives the vehicle togetherwith the electric motor. Such a parallel type hybrid electric vehiclehas a shortcoming in that its structure and control logic are relativelycomplicated compared to the series type. Nevertheless, since thisparallel type hybrid electric vehicle is efficient in that it utilizesthe mechanical energy of the engine and the electric energy of thebattery simultaneously, it is widely adopted in passenger cars, etc.

SUMMARY OF THE INVENTION

A method of controlling a battery charge level of a hybrid electricvehicle includes: monitoring a quantity of current accumulated for apredetermined time based on a battery charge/discharge current value;calculating a regenerative charge derating constant; calculating acorrection coefficient based on the quantity of current accumulated anda battery state of charge; multiplying the regenerative charge deratingconstant by the correction coefficient to calculate a final regenerativecharge derating constant; and multiplying the final regenerative chargederating constant by a charge power to calculate a final charge power,and selectively restricting the battery charge level based on the finalcharge power.

Calculating the correction coefficient may include setting thecorrection coefficient to a value smaller than 1 in an accumulatedcurrent quantity region corresponding to a rapid charge condition, andsetting the correction coefficient to 1 in an accumulated currentquantity region that does not correspond to the rapid charge condition.

An alternative method includes: monitoring a battery charge/dischargecurrent value; determining whether or not a continuous charge mode entrycondition is satisfied based on a charge current and an accumulatedcurrent quantity calculated by accumulating the monitored batterycharge/discharge current value at certain time intervals; entering acontinuous charge mode if it is determined that the continuous chargemode entry condition is satisfied, and calculating a regenerative chargederating constant, set as a value smaller than “1” according to aposition of a transmission gear and a battery state of chargecoefficient; multiplying the derating constant by a charge power tocalculate a final charge power, and restricting the battery charge levelbased on the final charge power.

Determining whether or not a continuous charge mode entry condition issatisfied may include determining that the continuous charge mode entrycondition is satisfied if a first condition and a second condition areboth satisfied, the first condition being a condition in which thecurrent quantity accumulated for a given time is smaller than apredetermined value, and the second condition being a condition in whichwhen a negative charge current for a given time is below a predeterminednegative value, a count is incremented, and a count value exceeds apredetermined count value every certain period.

The continuous charge mode entry may be banned if a current batterytemperature is below a predetermined temperature.

The continuous charge mode may be maintained until a continuous chargemode release condition occurs after the continuous charge mode.

When a negative charge current for a given time is below a predeterminednegative value, a count may be incremented, and it is determined whetheror not a count value is smaller than a predetermined count value everycertain period. If the count value is smaller than the predeterminedcount value continuously more than a predetermined frequency ofcondition occurrences, the continuous charge mode may be released.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be apparent from the following detailed description ofthe preferred embodiments of the invention in conjunction with theaccompanying drawings, in which:

FIG. 1 is a graph illustrating the charge/discharge control of a batteryaccording to the prior art;

FIG. 2 is a flowchart illustrating the process of finding a regenerativecharge derating constant in a method of controlling a battery chargelevel of a hybrid electric vehicle according to a first embodiment ofthe present invention;

FIG. 3 is a schematic diagram illustrating a logic configuration bywhich the restriction of the battery charge level is performed accordingto the present invention;

FIG. 4 is a timing chart graph illustrating an example of the case wherethe operation mode is switched to a continuous charge mode in a methodof controlling a battery charge level of a hybrid electric vehicleaccording to a second embodiment of the present invention;

FIG. 5 is a timing chart graphs illustrating an example of the casewhere the continuous charge mode is released in a method of controllinga battery charge level of a hybrid electric vehicle according to asecond embodiment of the present invention;

FIG. 6 is a graph a illustrating an example of a regenerative chargederating constant calculation map in a method of controlling a batterycharge level of a hybrid electric vehicle according to a secondembodiment of the present invention; and

FIG. 7 is a graph illustrating the effect of the restriction of thebattery charge level in a method of controlling a battery charge levelof a hybrid electric vehicle according to a second embodiment of thepresent invention.

DETAILED DESCRIPTION

A typical hybrid electric vehicle is equipped with a hybrid control unit(HCU) for controlling the overall operation of the vehicle. For example,the HCU includes an engine control unit (ECU), a motor control unit(MCU), a transmission control unit (TCU), a battery management system(BMS), a full auto temperature controller (FATC) for controlling theinterior temperature of the vehicle and the like.

These control units are interconnected via a high-speed CANcommunication line with the hybrid control unit as an upper controllerso that they mutually transmit and receive information.

In addition, the hybrid electric vehicle includes a high voltagebattery, or main battery, for supplying the driving power of theelectric motor. The high voltage battery supplies a needed power whilecontinuously charging and discharging during driving.

The high voltage battery supplies (discharges) electric energy duringthe motor assist operation and stores (charges) electric energy duringregenerative braking or engine driving. The battery management system(BMS) transmits the battery state of charge (SOC), available chargepower, available discharge power, etc., to the HCU/MCU to perform safetyand lifespan management of the battery.

Typically, a regenerative charge derating constant according to batterySOC and vehicle speed is calculated on the basis of a charge mode and adischarge mode, respectively, and then is finally multiplied by a chargepower so as to restrict the battery charge level.

Also, the BMS calculates a chargeable/dischargeable power in real timein consideration of battery temperature, battery SOC, etc. Severalexamples of power reduction control depending on each variable are asfollows (see FIG. 1):

1. Power reduction control depending on the battery temperature: If thebattery temperature rises, the BMS carries out a control of reducing thechargeable/dischargeable power of the battery.

2A. Power reduction control depending on the battery SOC: If the batterySOC increases, the BMS carries out a control of reducing the chargeablepower of the battery.

2B. Power reduction control depending on the battery SOC: If the batterySOC decreases, the BMS carries out a control of reducing thedischargeable power of the battery.

However, the control of a battery charge level of a hybrid electricvehicle according to the prior art encounters the following problems.

First, conventionally, only the battery SOC and the vehicle speed aretaken into consideration as factors for finding the derating constant,so that the battery temperature rises by a battery chemical reaction dueto a large quantity of electric charge, measured in Ampere-hours (Ah),during battery charging.

Conventionally, such a temperature rise is not properly corrected for,and if a battery cooling fan does not work, such as when the vehicle isparked after downhill driving (being charged in a large quantity ofelectric charge), the battery temperature reaches a dangerous level, sothat a hybrid functions (motor assist, motor start, etc.) are notperformed normally.

Especially when the vehicle is parked after the battery is continuouslycharged at high power during mountainous downhills, the batterytemperature rises excessively due to the latent heat of the batteryduring parking.

Reference will now be made in detail to the preferred embodiment of thepresent invention, examples of which are illustrated in the drawingsattached hereinafter, wherein like reference numerals refer to likeelements throughout. The embodiments are described below so as toexplain the present invention by referring to the figures.

In the first embodiment shown in FIGS. 2 and 3, a restriction of thecharge power of a high-voltage battery (main battery) is controlleddepending on the accumulated current quantity to prevent an excessiverise in the battery temperature due to the rapid charge of the battery.

That is, the current quantity (i.e., an integral value of the quantityof electric charge over time, measure in Ampere-hours [Ah]) accumulatedfor a predetermined time is monitored. When rapid charge progressesduring which the integral value is below a predetermined level, acorrection coefficient according to the accumulated current quantity isapplied to a final regenerative charge derating constant calculation endto restrict a charge power. In this manner, the charge power isrestricted depending on the accumulated current quantity according to avehicle traveling condition to thereby prevent an excessive rise in thebattery temperature due to the rapid charge of the battery and theinterruption of a hybrid function due to the excessive rise in thebattery temperature.

Herein, the term “current quantity” refers to an instantaneous currentvalue detected from a current sensor at the time of the batterycharge/discharge, and the accumulated current quantity is positive (+)at the time of the uphill traveling of the vehicle and negative (−) atthe time of the downhill traveling of the vehicle.

In the first embodiment, a regenerative charge derating constantaccording to the battery SOC and the vehicle speed is calculated in acharge mode. This may be done in any known manner. Then a correctioncoefficient according to the accumulated current quantity isadditionally applied to the calculated derating constant to find a finalregenerative charge derating constant, which is used to calculate acharge power.

A charge power, calculated by a separate logic, is multiplied by a finalregenerative charge derating constant (a value smaller than 1) tothereby restrict the battery charge level. In the first embodiment ofthe present invention, a charge power calculated by a separate logic ismultiplied by a final regenerative charge derating constant obtained byadditionally applying the accumulated current quantity to therebycalculate a final charge power, and the battery charge level isrestricted, i.e. the calculated final charge power is applied to thebattery charge.

A process of controlling a battery charge level of a hybrid electricvehicle according to the first embodiment of the present invention willbe described hereinafter in more detail.

First, a current quantity accumulated for a predetermined time (forexample, for 1 second) is calculated and monitored from a batterycharge/discharge current value that is input from a current sensor. Atthis time, the battery SOC and the vehicle speed are monitored.

Further, a regenerative charge derating constant is found from a chargemode derating constant calculation map according to a battery SOC and avehicle speed in a charge mode (charge mode flag value of “1” is input)and is found from a separate discharge mode derating constantcalculation map according to a battery SOC and a vehicle speed in adischarge mode during driving.

Also, in the present invention, the regenerative charge deratingconstant found in the above step is multiplied by a correctioncoefficient (a value less than 1) calculated from a correctioncoefficient calculation map according to the monitored accumulatedcurrent and the battery SOC to calculate a final regenerative chargederating constant.

The correction coefficient calculation map corrects the deratingconstant in a rapid charge condition. The correction coefficient is lessthan 1 in an accumulated current quantity region corresponding to therapid charge condition, and is equal to 1 in an accumulated currentquantity region that does not correspond to the rapid charge conditionin the correction coefficient calculation map.

Thus, the regenerative charge derating constant found in the above stepis multiplied by a correction coefficient smaller than “1” in theaccumulated current quantity region corresponding to the rapid chargecondition, so that a regenerative charge derating constant smaller thanthe regenerative charge derating constant found from the deratingconstant calculation map is determined as a final regenerative chargederating constant. On the other hand, the regenerative charge deratingconstant found from the derating constant calculation map is determinedas a final regenerative charge derating constant as it is in theaccumulated current quantity region that does not correspond to therapid charge condition.

As such, when the accumulated current quantity falls within the rapidcharge condition, the final regenerative charge derating constantcorrected by the correction coefficient is multiplied by a charge powercalculated by separate logic to thereby calculate a final charge power.

Resultantly, when the final charge power is calculated, the batterycharge level of the vehicle is restricted based on the calculated finalcharge power. The restriction of the battery charge level of the vehicleprevents excessive rise in the battery temperature due to the rapidcharge of the battery.

Now, a process of controlling a battery charge level of a hybridelectric vehicle according to a second embodiment of the presentinvention will be described hereinafter in more detail.

In the second embodiment of the present invention, a batterycharge/discharge current value input from a current sensor is monitored.Then, whether or not the vehicle is on a continuous downhill isdetermined based on the battery charge/discharge current value. If it isdetermined that a continuous downhill condition is satisfied, thebattery charge level is restricted.

In more detail, first, a charge/discharge current (Ah) detected by thecurrent sensor is monitored and a position of a transmission gear and abattery OSC is monitored during the traveling of the vehicle.

Also, if a continuous charge mode entry condition is satisfied, it isdetermined that the vehicle is on a continuous downhill section. Thecontinuous charge mode entry condition may be as follows:

Continuous Charge Mode Entry Condition

1. First Condition for Continuous Charge Mode Entry:

First, the monitored battery charge/discharge current (Ah) value isaccumulated every certain time interval and an accumulated currentquantity is calculated. If the current quantity accumulated for a giventime is smaller than a predetermined value, the program determines thatthe battery is in the continuous charge mode.

That is, during typical battery charge/discharge, an instantaneouscurrent value detected from the current sensor represents a negative (−)value in case of charge and represents a positive (+) value in case ofdischarge. This current value is accumulated every certain time interval(for example, one minute) and the accumulated current quantity iscalculated. As shown in FIG. 4, the first condition for the continuouscharge mode entry is satisfied if the current quantity accumulated for agiven time (for example, two minutes) is smaller than a predeterminedvalue (for example, −0.26 A)(the accumulated current quantity <−0.26 A).

2. Second Condition for the Continuous Charge Mode Entry:

If when a charge current for a given time is below a predeterminedvalue, a count is incremented, and a count value exceeds a predeterminedcount value every certain period, the program determines that thebattery is in the continuous charge mode. In case of the charge by anengine driving force but not a regenerative charge, the count is notincremented. On the other hand, if a regenerative charge current duringthe regenerative charge is more than a predetermined value, the count isincremented.

That is, the second condition for the continuous charge mode entry issatisfied if when the regenerative charge current for a given time (forexample, 100 ms) is smaller than a predetermined value (for example, −7A) (regenerative charge current ≦−7 A), a count is incremented and, asshown in FIG. 4, a count value exceeds a predetermined count value (forexample, 330) (count value >330) every certain period (for example, oneminute).

As shown in FIG. 4, only if the aforementioned two conditions for thecontinuous charge mode entry are satisfied, the program enters thecontinuous charge mode, and it is determined that the vehicle is on acontinuous downhill.

In this case, as a continuous charge mode entry ban condition, if acurrent battery temperature is below a predetermined temperature (forexample, 35° C.), the continuous charge mode entry is banned.

In addition, after the program enters the continuous charge mode, thecontinuous charge mode is maintained until there occurs a continuouscharge mode release condition which will be described later.

The continuous charge mode entry condition is satisfied, as shown inFIG. 6, a regenerative charge derating constant is calculated from aregenerative charge derating constant calculation map.

Referring to FIG. 6, during general driving, a regenerative chargederating constant is set as “1” so that a battery charge level of thevehicle is not restricted. But if it is determined that the continuouscharge mode entry condition is satisfied, the program enters acontinuous charge mode and calculates a regenerative charge deratingconstant set as a value smaller than “1” according to a current position(“D”, “L”) of a transmission gear and a battery OSC coefficient (valueaccording to the current battery SOC).

Also, a charge power, calculated by separate logic, is multiplied by thefinal regenerative charge derating constant to thereby calculate a finalcharge power, and then the calculated final charge power restricts thebattery charge level. Thus, in such a continuous charge mode,restriction of the battery charge level can prevent an excessiveincrease in battery temperature.

Continuous Charge Mode Release Condition

In a continuous charge mode release condition, when a charge current fora given time is below a predetermined value, a count is incremented, andit is determined whether or not a count value is smaller than apredetermined count value every certain period. If a condition in whichthe count value is smaller than the predetermined count valuecontinuously occurs more than a predetermined frequency of conditionoccurrences, the continuous charge mode is released.

That is, if when the regenerative charge current for a given time (forexample, 100 ms) is smaller than a predetermined value (for example, −7A) (regenerative charge current ≦−7 A), a count is incremented and, asshown in FIG. 5, it is determined whether or not a count value issmaller than a predetermined count value (for example, 220) (count value<220) every certain period (for example, one minute). If a condition(count value <220) in which the count value is smaller than thepredetermined count value continuously occurs more than a predeterminedfrequency (for example, three times) of condition occurrences, thecontinuous charge mode is released.

As such, when the continuous charge mode release condition is satisfied,the battery charge level of the vehicle is not limited, as in generaldriving.

In case where a vehicle travels along a continuous downhill travelingsection so that a continuous charge is performed with high power, thecharge is restricted to thereby prevent excessive increase in batterytemperature during parking of the vehicle.

The result identified through a test of the effect of the restriction ofthe battery charge level is shown in Table 1 below. In Table 1, the casewhere a battery charge level restriction logic is not applied and thecase where a battery charge level restriction logic is applied arecompared with each other.

As can be seen from Table 1 below, when restriction logic is applied,excessive increase in battery temperature is prevented after a key-offoperation. All tests in Table 1 were conducted under an ambienttemperature of 35° C.

TABLE 1 Temperature just before key-off Temperature after key-off(° C.)(° C.) 10 min 30 min 60 min 130 min Restriction logic not applied 47 5765 71 76 Restriction Chamber 44 46 50 53 58 logic applied test resultField test 39 39 42 42 50 result

As described above, the method of controlling a battery charge level ofa hybrid electric vehicle according to embodiments of the presentinvention has the following advantageous effects.

First, a battery charge/discharge current value based on a batterycharge/discharge current value is monitored, and when the rapid chargeprogresses during which the integral value is below a predeterminedlevel, a correction coefficient according to the accumulated currentquantity is applied to a final regenerative charge derating constantcalculation end to restrict a charge power, to thereby prevent anexcessive rise in the battery temperature due to the rapid charge of thebattery and the interruption of a hybrid function due to the excessiverise in the battery temperature.

Second, a battery charge/discharge current value is monitored, andwhether or not a vehicle is on a continuous downhill section isdetermined based on the monitored battery charge/discharge currentvalue. If it is determined that a continuous downhill condition issatisfied, the battery charge level is restricted to prevent excessiverise in the battery temperature.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

1. A method of controlling a battery charge level of a hybrid electricvehicle, the method comprising: monitoring a battery charge/dischargecurrent value; determining whether or not a continuous charge mode entrycondition is satisfied based on a charge current and an accumulatedcurrent quantity calculated by accumulating the monitored batterycharge/discharge current value at certain time intervals; entering acontinuous charge mode if it is determined that the continuous chargemode entry condition is satisfied, and calculating a regenerative chargederating constant, set as a value smaller than “1” according to aposition of a transmission gear and a battery state of chargecoefficient; multiplying the derating constant by a charge power tocalculate a final charge power, and restricting the battery charge levelbased on the final charge power.
 2. The method of claim 1, wherein thestep of determining whether or not a continuous charge mode entrycondition is satisfied comprises determining that the continuous chargemode entry condition is satisfied if a first condition and a secondcondition are both satisfied, the first condition being a condition inwhich the current quantity accumulated for a given time is smaller thana predetermined value, and the second condition being a condition inwhich when a negative charge current for a given time is below apredetermined negative value, a count is incremented, and a count valueexceeds a predetermined count value every certain period.
 3. The methodof claim 1, wherein the continuous charge mode entry is banned if acurrent battery temperature is below a predetermined temperature.
 4. Themethod of claim 1, wherein the continuous charge mode is maintaineduntil a continuous charge mode release condition occurs after thecontinuous charge mode.
 5. The method of claim 1, wherein when anegative charge current for a given time is below a predeterminednegative value, a count is incremented, and it is determined whether ornot a count value is smaller than a predetermined count value everycertain period, and if the count value is smaller than the predeterminedcount value continuously more than a predetermined frequency ofcondition occurrences, the continuous charge mode is released.